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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-Q/A

(Amendment No. 1)

(Mark One)

For the quarterly period ended June 30, 2014

or

For the transition period from:              to             

Commission File Number 000-21937

CERUS CORPORATION

(Exact name of registrant as specified in its charter)

(925) 288-6000

(Registrant’s telephone number, including area code)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15 (d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    YES  x    NO  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    YES  x    NO  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    YES  ¨    NO  x

As of July 25, 2014, there were 74,048,000 shares of the registrant’s common stock outstanding.

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CERUS CORPORATION

AMENDMENT NO. 1 TO QUARTERLY REPORT ON FORM 10-Q/A

THREE AND SIX MONTHS ENDED JUNE 30, 2014

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EXPLANATORY NOTE

Cerus Corporation (the “Company”) is filing this Amendment No. 1 to Quarterly Report on Form 10-Q/A (this “Amendment”) to amend the Company’s Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2014, as filed with the Securities and Exchange Commission (the “SEC”) on August 8, 2014 (the “Original 10-Q”). This Amendment is being filed solely to re-file Exhibit 10.2 to the Original 10-Q in response to comments received from the staff of the SEC relating to a confidential treatment request that the Company submitted with respect to Exhibit 10.2 to the Original Filing, and in connection therewith, to amend Part II, Item 6 of the Original 10-Q and the Exhibit Index to the Original 10-Q. In addition, as required by Rule 12b-15 under the Securities Exchange Act of 1934, as amended, new certifications by the Company’s principal executive officer and principal financial officer are filed as exhibits to this Amendment.

No attempt has been made in this Amendment to modify or update the other disclosures presented in the Original 10-Q. This Amendment does not reflect events occurring after the filing of the Original 10-Q (i.e., those events occurring after August 8, 2014) or modify or update those disclosures that may be affected by subsequent events.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

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EXHIBIT INDEX

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